The present invention relates to an image forming apparatus, and particularly to an image forming apparatus which can detect a sheet on which an image is to be formed and can transport the sheet without staining it with toner and deteriorating image quality.
Heretofore, an image forming apparatus which forms an image with toner on transportation paper has been known. In this image forming apparatus, generally a laser beam is scanned on a photoconductor on the basis of image data thereby to form an electrostatic latent image on the photoconductor. The electrostatic latent image on the photoconductor is developed with toner and made visible to form a toner image, the toner image is transferred onto the transportation paper, and thereafter the transportation paper is pressed by a heat roller thereby to fix the toner image.
In this image forming apparatus, in order to transport paper in synchronization with image forming processing, a mechanism of detecting paper to be transported is arranged at each section of the apparatus. For example, a turn lever is arranged in a position where the transportation paper comes into slide-contact, and a turn of the turn lever by the transportation paper is detected by a sensor such as a switch.
As such the paper detecting mechanism, for example, a paper detecting mechanism of a image forming apparatus provided on the downstream side of a fixing section which fixes the toner image has been proposed. The paper detecting mechanism includes a rotator, which is provided at a leading end of the slide-contacting turn lever, for rotating by slide-contact with the transportation paper in order to reduce generation of static electricity in the transportation paper due to the slide-contact with the turn lever, or generation of damage and wear (for example refer to JP-A-2000-72282 and J P-A-2000-72284).
However, in such the related image forming apparatus, it is necessary to arrange the paper detecting mechanism also between a transfer section which transfers the toner image onto the transportation paper and the fixing section which fixes the toner image onto the transportation paper.
The toner image transferred onto the transportation paper, which is transported between the transfer section and the fixing section, is fixed yet. Therefore, there is fear that the toner is easily scattered and image quality deteriorates, and further when the floating toner in the air attaches and accumulates on the turn lever, the transportation paper which comes into slide-contact with the turn lever is stained with the toner. Specifically, in case that the turn lever is formed of a material which is charged negatively by the slide-contact with the transportation paper, and the toner is charged negatively, the toner on the transportation paper which has not been fixed yet repels to the turn lever so that a white streak (toner deletion) is occurred in the image. Further, in case that the turn lever is formed of nylon resin having strong positive charge acceptance, the floating toner in the surrounding atmosphere is attracted to the turn lever so that the floating toner is attached and accumulated onto the turn lever, whereby a leading end portion of the transportation paper, which firstly comes into slide-contact with the turn lever is stained with the toner.
Therefore, even if, the paper detecting mechanism, having the turn lever and the rotator provided on a leading end of the turn lever, is located between the transfer section and the fixing section, in spite of the presence or absence of the rotator, there is fear that the toner on the transportation paper scatters so that the image quality is deteriorated, or the toner is positively attached and accumulated on the turn lever so that the transportation paper is stained with the toner. It is difficult to simultaneously remove the image deterioration and the paper stain with high reliability.